Horizontal precedent can either stabilize law or accelerate legal change.

Evidence

Considerably more important is the influence of state courts in other states. … Reliance on precedent contributes to stability in the law when the rulings in various states coincide. But when they diverge, state courts’ reliance on precedent can, paradoxically, be a force for legal change. — G. Alan Tarr, Judicial Process and Judicial…, 3534

Categorization

• DEEPTHINKING: A genuine paradox: the same institution that anchors the law can be the engine of its transformation, depending on whether sister-state rulings converge or split.
• XREF: Explains the mechanism behind policy diffusion across states — the engine of same-sex-marriage and school-finance litigation trajectories described earlier in the chapter.